Pyrazolotriazole dye-forming magenta couplers are well known in the color image-forming coupler art. Such couplers provide magenta dyes with superior dye light stability. This class of couplers often require multi-step synthetic sequences, involving moisture sensitive intermediates such as imidates, resulting in lower overall yields. The present invention relates to a process of preparing N-(4-substituted pyrazolyl)amidines (I) which are useful key intermediates in the preparation of PT coupler compounds of the formula (II). ##STR1##
Formula (II) represents pyrazolotriazole compounds which are PT dye-forming magenta couplers employed in photographic silver halide materials. In the above formulae (I) and (II), X is a coupling-off group and R.sub.1 and R.sub.2 are independently hydrogen or a coupler substituent known in the photographic art which does not adversely affect the desired properties of the coupler. Pyrazolotriazoles of formula (II) can be obtained from the amidines of formula (I) by methods known in the art.
The methods known in the art for the synthesis of amidines involve the reaction of the organic nitrile with a suitable alcohol in the presence of anhydrous hydrogen chloride to form the imidate ester, which on subsequent reaction with a 3-amino-4-substituted-5-alkylpyrazole furnished the desired amidine. ##STR2##
Unfortunately, this process involves the isolation and manipulation of rather unstable and highly moisture sensitive intermediate imidate esters (IV).